The invention refers to a laser applicator with an elongate catheter comprising an inner core and a cladding surrounding the core, wherein the cladding comprises a series of openings in a decoupling portion, whose opening surface increases towards the distal end.
Such a laser applicator is described in US 2009/0275931 (Vimecon), the disclosure of which is incorporated into the present application by reference. The known laser applicator comprises an elongate flexible catheter including a light guide. The distal end section is formed into a lariat-like shape whose plane extends transversely to the main portion of the catheter. Laser radiation is input into the light guide at the proximal end. A decoupling portion exists at the distal end of the catheter, where the energy is coupled laterally out of the light guide and exits from the catheter.
In particular, the laser applicator serves for the treatment of atrial fibrillation and other types of cardiac arrhythmia. It can be used to cauterize cardiac tissue by converting light energy into thermal energy. The laser radiation exiting the light guide heats the surrounding tissue to values above 60° C., resulting in the denaturation of proteins and the formation of an electrically inactive scar. For the purpose of achieving a uniform distribution of the decoupled energy over the length of the decoupling path, the width of the circular cladding segment that causes the decoupling can be varied over the decoupling path.
DE 10 2006 039 471 B3 describes a laser applicator comprising a catheter with a light guide. In a distal end section of the catheter, the cladding of the light guide has a cutout from which light exits laterally from the light guide. While the intact cladding of the light guide effects total internal reflection so that the light energy is transported in the longitudinal direction of the light guide, the cutouts at the border of the light guide core cause refraction so that light energy is coupled out. The cutouts are discrete openings of round cross section. Their diameter increases constantly from one opening to the next in the direction of the distal end of the light guide and varies from a size of 20 μm for the first opening to a size of 100 μm for the last opening. In a certain variant, the distances between two respective neighboring openings decrease in the direction of the distal end of the light guide fiber. This is to compensate for the decrease in radiance in the light guide fiber in the direction of its distal end.
Providing the openings for the lateral decoupling of laser energy from the light guide requires high precision, wherein the enlargement of the exit surface must be made in very small increments from the distal end to the proximal end.
The present application addresses the problem of making a decoupling path in a light guide by opening the cladding of the light guide in order to achieve an energy density of the decoupled radiation that is uniform over the length of the decoupling portion.